1. Field of Invention
This invention relates to a method of forming a photoreceptor by spray coating one or more layers of the photoreceptor using ink jet nozzles. More in particular, the invention relates to a method of forming one or more layers of a photoreceptor containing polymer binder by spray forming the layers with ink jet nozzles, and to a printing machine containing a photoreceptor so formed.
2. Description of Related Art
Manufacturing of organic photoconductor drums used in current laser or LED printers and copiers is accomplished almost exclusively by dip coating. Spray coating is also used, albeit on a limited basis, for example in forming Broad Organic Spectrum (BOS) photoreceptors.
U.S. Pat. No. 5,906,904, incorporated by reference herein in its entirety, describes an electrophotographic imaging member. In describing the imaging member, it is indicated in this patent that each of the layers of the imaging member may be formed by conventional techniques such as spraying, dip coating, draw bar coating, gravure coating, roll coating, and the like.
Numerous problems are encountered in the operation of conventional spray or dip coating processes. In particular, material related difficulties are among the more challenging problems that need to be addressed.
In the manufacture of a multi-layer drum photoconductor (OPC) by dip coating, large volumes of coating solutions are required for application of each layer. The respective solutions are held in storage tanks and recirculated through cylindrical reservoirs in which the drum substrates are immersed. For the simultaneous coating of multiple drums in a single operation, multiple reservoirs are fabricated in rectangular or circular arrays for the application of a single layer at a dip coating process station, it is typical to have a total volume of 20 to 100 gallons of coating solution recirculating continuously through the coating fluid delivery system. This is problematic with respect to maintaining inventory of a large volume of expensive materials, with risk of loss due to contamination, limited shelf life for a majority of coating formulations, and difficulty in maintaining steady state composition of the coating solution due to solvent evaporation.
Dip coating also has other operational problems. The process requires a bottom edge wiping process step for each layer coating. This step produces additional solvent vapor emissions, a liquid solvent waste stream, and slows the process cycle time. Alternative end cleaning processes such as laser ablation also have associated problems. Furthermore, dip coating photoreceptor devices have a thickness taper, commonly known as sloping, at the upper end of the substrate where the coating process is initiated.
The use of air spray coating for manufacturing photoreceptors, and the recent development of rotary atomization spray coating for wide format OPC drums, also possess material related problems. Transfer efficiencies may be as low as 20%, resulting in excessive material consumption and solvent vapor emissions per unit of production. The droplet size distribution of spray atomizing devices is broad, and the arrival of droplets at a substrate surface is chaotic. This results in a non-homogeneous, i.e., grainy, coated layer on a microscopic scale, and a mottled coating appearance on a macroscopic scale. The spray patterns for both air spray and rotary spray coating are fan shaped, and the spray fan must be scanned beyond the end of the substrate in order to achieve a uniform coating along the full length of the substrate. This thus requires that the ends of the substrate be masked or that an edge wiping step be used (with the disadvantages described above). In addition, the substrate fixture and hardware and the interior of the coating chamber must be periodically cleaned, which cleaning operations are difficult to perform without increasing cycle time and producing waste streams and/or vapor emissions.
U.S. Pat. No. 5,550,618 underscores the problems associated with conventional spray coating techniques. It is indicated therein that coatings applied by spray coating are often uneven, and that coatings having an uneven thickness do not have uniform electrical properties, thereby degrading the print quality.
Conventional spray coating processes, including rotary atomization spray coating processes, do not use ink jet nozzles in the process.